The present invention generally relates to programmable thermostats and, more particularly, to an electronic programmable thermostat for a heating and cooling system having an oscillation control mechanism.
Programmable thermostats have greatly increased the degree to which a user can control air conditioning systems. "Air conditioning system" as used herein will generally refer to both heating and cooling systems. Programmability permits users to program a plurality of temperature settings for a plurality of program times. Programmability permits high efficiency operation and can result in substantial energy savings. For example, if an air conditioning system is utilized to control the temperature of a personal residence, the on/off switching of the air conditioning system may be precisely determined. It is desirable to have the residence controlled to a comfort temperature during times of occupancy, but in the interest of energy conservation, it is further desirable to have the system control the ambient temperature to some temperature other than the comfort temperature during other times.
In a particular example, a user may program his thermostat such that the cooling system may be switched on at 5:00 P.M. to cool the residence to the program temperature of 78.degree. by 6:00 P.M. when the user returns home from work. The program temperature of 78.degree. may be maintained by the thermostat until 11:00 P.M. when the occupants go to bed. The air conditioner then may be programmed to maintain the house at 76.degree. overnight. From 7:30 A.M. to 9:00 A.M., it may be desirable to have the temperature controlled to 78.degree.. The temperature then may be set up to 85.degree. during the day from 9:00 A.M. to 5:00 P.M. in order to conserve energy. It is important that the temperature not be permitted to rise too much during the unoccupied periods or else the system may require so much energy to bring the ambient temperature to the program temperature that energy savings are eliminated. A similar schedule may be programmed for the heating system during wintertime.
Various programs may be created and modified to suit user lifestyle. Different programs may be entered to control the air conditioning system over weekends when a user is likely to be home at different hours.
A single thermostat may, in some instances, be programmed with both a heating and a cooling program schedule. In some situations, it is desirable to control the ambient temperature in a temperature controlled region over a rather small temperature range. This may require setting the heating and cooling control temperatures close to one another. Such settings, while providing the precise temperature control required, can also result in rapid oscillation between heating and cooling systems. This rapid oscillation is undesirable and inefficient and can cause damage to both the heating and cooling systems.